Volume control apparatus and method



pril 14, 1936.

A. R. HOPKINS VOLUME CONTROL APPARATUS AND METHOD Filed April 25, 1933 2 Sheets-Sheet 1 'INVENTOR ALVA A HOPKINS BY 7 ATTORNEY April 1936. A. R. HOPKINS VOLUME CONTROL APPARATUS AND METHOD ZSheets-Sheet 2 Filed' April 25, 193-3 I INVENTOR ALVA. HOPKINS BY )Yg ATTORNEY Patented Apr. 14, 1936 UNITED STATES VOLUME CONTROL APPARATUS AND METHOD Alva It. Hopkins, Merchantville, N. J., assignor to Radio Corporation of America, a. corporation of Delaware Application April 25, 1933, Serial No. 667,825

15 Claims. (Cl. 179-10011) This invention relates to an apparatus and method for controlling thevolume level of one or more sources of audio frequency energy either separately or collectively.

Another object of the invention is to combine in the output of the apparatus, audio frequency currents arising in two different sources and to control the relative amounts or values of the two currents. I

A still further object is to provide an attenuator arrangement whose .output impedance remains substantially constant during its adjustment over a range of values.

Other objects of the invention will appear-as the description thereof proceeds. For a better understanding of the invention reference is made to the attached drawings wherein one embodiment thereof is shown but it will be understood that the invention is not to'be limited by the specific form shown but is intended to apply to any apparatus or method coming within the scope of the appended claims.

In the drawings,

Figure 1 is a schematic diagram of the input circuits and attenuator connections;

Figure 2 is a schematic diagram showing the relative radial arrangement of the elements of the attenuator; and,

Figure 3 is a cross sectional view of the control shaft and arms of the attenuator.

Referring first to Figure 1 a phonograph A having a pick-up l of any desired type may have a volume control resistor 2 across the movable contact 3 and one end of which the primary of an audio transformer E is connected. The secondary terminals 5 of E are connected by the leads shown to the midpoints-of the top end sections 6 of the attenuator resistors D, the midpoint of the secondary of E being preferably grounded as shown. A microphone B of any desired type may be coupled to an audio transformer F to the secondary terminals 5 of which the midpoints of the center sections I of resistors D are connected by the leads shown.

A radio receiver C of any preferred type which is tunable over the present broadcasting range V and which includes any known type of volume control device, either of the manual or of the automatic type, may be connected to a receiving antenna G. As the elements of such a radio receiver are well known, it is not necessaryto illustrate them in detail but I have shown schematically the plate circuit of the last audio stage, or in certain cases the power detector tube, of such a receiver connected by an audio transformer H, having its primary 9 in said ,plate circuit, to the midpoints of the lower vencl sections 8 of resistors D. The secondary of H has a center tap, similar to transformers E and F,

which is preferably grounded as shown. I prefer 5 to so design transformers E, F and H that their impedances, when connected to the signal'sources, as measured across their secondary terminals 5, 5 are all equal. When so arranged either input signal source may be substituted for the other 10 without interfering with orupsetting the impedance relations within the attenuator. In an embodiment of the invention I have made each section 6, 1 and 8 of resistors D of high resistance wire having a resistance of 800 ohms and '15 the ends of the respective sections connected together by leads Ill and II which are grounded, as shown, in any preferred manner. The resistance between the midpoints to which the terminals 5 are connected and ground, isthus 400 ohms.

Alongside of sections 6, l and 8 and preferably parallel therewith I mount resistor sections l2, I3, l4, l5, l6 and I1 which are slightly separated as shown and each of which may be made of resistance wire and have a resistance value of '25 400 ohms. The midpoints of each of the sections 2, l3 and M are connected together by lead l8 which is connected to one of the output terminals IQ of the attenuator by a lead 20. Mounted adjacent the upper half of resistor l2 and pref- 30 erably parallel therewith are metallic strips 2| and 22, two similar strips 23 and 24 being mounted adjacent the lower end of resistor l4. Strips 2| and 23 are conductively connected to lead l8 while strips 22 and 24 are connected to- 5 gether by a lead 25 which is connected to the midpoint of resistor 'l' by lead 26. The midpoints of resistors l5, l6 and I! are connected together and to the other output terminal I9 by lead 21 g which also connects to metallic strips 28 and 29 40 resistors l5, l6 and H as shown. Mounted preferably'on the same arm 38 as 34 is a metallic contact or connector 35 which is slidable alon and arranged to contact strips 23 and 24 or strips 2| and 22. Mounted on the same arm 39 as carries contact 35 is a contact 31 which is ar- 5 ranged to connect strips 28 and 30 or strips 29 and 3|. Arms 38 and 39 are indicated as being connected for uni-control operation by a common shaft 40 but it is not necessary to my invention that they be mounted on the same shaft as they may obviously be mounted. on two separate shafts which are geared together in a known manner.

In the operation of the device, when a radio signal has been tuned in and the set adjusted to the desired volume level, the full output voltage of the set will be applied to the center points 4| and 42 of resistors 8, these points having a maximum A. C. potential difference. This full potential is applied by contacts 34 and 35 through leads and 21 to the output terminals 19, resistors I 4 and I! not being in the circuit traversed by the current. As shaft 48 is operated to raise the contacts along 8 the voltage difference be.

tween contacts 34 and 35 decreases and when the upper ends of 8 are reached, as these points .are grounded, the voltage applied to output terminals .19 will bezero. It will also be noted that as contacts .34 and 35 are moved upwards from points 4| and '42 more and more of resistors I4 "and I! are included in the output circuit. Resistance 8 is reducedso that its impedance is kept substantially the same as the voltage ap- :plied to it is decreased.

If the phonograph A, microphone B and radio receiver C are simultaneously applying signal energy to the attenuator and it is desired to apply radio signals only to the output terminals,

contacts "34 and 35 will be operated over the top halves of resistors '8 as just explained to control the radio output volume level. But if it is desired to apply speech energy from the microphone also to the output terminals, upon lowering the contacts to a position just below that shown in Fig. 1 contacts 36 and 3! will close the circuits across strips 23, 24 and 28, 30 thereby applying the full speech energy from B to the output terminals. As the set of contacts is further lowered along the lower portions of resistors '8 less and less radio energy will be applied to the terminals 19 but the speech energy will remain constant as contacts 36 and 31 move along their respective strips. In other words as the contacts are adjusted lower below terminals 4| and 42 the radio signal may be progressively faded out in the output circuit of the mixer while the speech energy level remains constant, the relative proportion of speech and radio signal in the output circuit being varied as desired.

When phonograph signals only are desired in the output circuit l9, contacts 34 and 35 may be set at the middle of resistors 6 and the contact '3 adjusted to produce the desired maximum output phonograph signal level at terminals l9. After this adjustment of 3 the phonograph volume is reduced as desired'by moving contacts 34,

'36, 35 and 31 towards the lower ends of resistors 6, -l2 and I5. If it is desired to mix the speech and phonograph signal energies, the contacts are adjusted to a position just above the midpoints of resistors 6, when contacts 35 and 31 will contact strips 2|, 22 and 29, 3| respectively to transmit the full speech energy of B to the output circuit 19, the phonograph energy also being at subs'tantially maximum. As the contacts 34 and 35 are raised along the resistors, the phonograph signal voltage or potential between them is grad ually decreased while the speech energy in the output circuit remains at substantially its maximum value. In other words, by adjusting the contacts along the upper portions of resistors 6, the phonograph signals may be faded out on the speech signals.

When it is desired to apply speech signals only of any desired level or value to the output circuit i9, shaft 40 is adjusted to bring contacts 34 and 35 in contact with resistors I, I3 and I 6, the output speech signals being a maximum when the contacts are at their midpoints and decreasing in value as the contacts approach either grounded end of I. Also as the grounded end is approached the impedance of the output circuit is increased by reason'of more of resistance units [3 and It being included in the circuit.

As shown diagrammatically in Fig. 2 and in cross section in Fig. 3, the several resistor units may be arranged on the arcs of circles, the resistance wire 43 composing them being wound on arcuate'insulating strips 44 and 45 mounted concentric with shaft 40. If preferred the elements of the attenuator o-r mixer may be mounted within 'a metal casing 43 the open end of which may be closed by a metal cover 41, the shaft 40 being journaled in thecasing and projecting through an aperture 48 within an upright or vertical panel 56, the casing being supported on the panel in any well known manner, not shown. The contact strips 2| to 24 of one attenuator section may be mounted on an insulating support 45 mounted within the casing in any preferred manner, not shown. An arm 49 of insulating material may carry near its end the metallic contact 36 to connect strips 23 and 24 and a second metallic contact '34 which connects the several resistor elements shown in Fig. 1. A second insulating arm 50 secured to shaft 43 carries metallic contact 31 which serves to connect strips 28, 30 or 29 and 3|. These strips are mounted on an insulating support 5| in any preferred manner and arranged in circular arcs in the same way as 'strips Z I to 24 as shown in Fig. 2. The resistor sections 6, I and 8 are wound of resistance wire 43 on an insulating circular strip 52, resistor sections l5, l6 and I! being similarly wound on circular insulating strip 53. Strips 52 and 53 may be supported by the casing 46 in any known "manner, not shown. While I have described the resistor elements of the mixer as being formed of high resistance wire, it will be understood that my invention is not limited to this as other well known forms of resistor elements such as carborundum, graphite etc. may be used in place of wire. I

For conveniently controlling the attenuator, the shaft 40 may have a control knob 55 secured to its end as shown. If signals from the three sources shown are being impressed simultaneously on the attenuator or mixer, by operating the single knob 55 the operator may secure in the output circuit 19 either radio, speech or phonograph signals alone and of any desired amplitude or he may cause the speech signals at constant volume level to be impressed on or mixed with either radio or phonograph signals of any desired volume level. The mixer permits a singer to be accompanied by music recorded on a phonograph record or coming in over a radio set but my invention is not limited to such use as other obvious uses will suggest themselves to those skilled in the electro-acoustic art. The output terminals l9 may be connected directly to a telephone, loudspeaker or a telephone line or they may be connected to a vacuum tube audio frequency amplifier of any known type if amplification of the output currents of the mixer are desired.

Having described my invention, what I desire to secure by Letters Patent is:

1. An attenuator comprising four resistor elements, an input circuit connected to the midpoints or electrical centers of two of said resistors, an output circuit connected to the midpoints or electrical centers of the other two resistors and two movable contacts adapted to be adjusted along said resistor elements.

2. The combination of the preceding claim in which the ends of the resistors connected to the input circuit are conductively connected.

3. In a device of the class described, the combination of two resistor elements, means for maintaining the ends of said resistors at the same potential, means for impressing audio frequency voltages on said resistors, two other resistors mounted adjacent said first named resistors and means connecting said first and second named resistors including at least one adjustable contact.

4. In a device of the class described, the combination of two circuit elements having substantial impedance, means for grounding the ends of said elements, a second pair of circuit elements having substantial impedance, means connecting one of said first to one of said seco-nd'named circuit elements and adjustable means connecting the other of said first to the other one of said second named circuit elements whereby a variable voltage may be secured across said first named and said adjustable connecting means when a constant voltage is applied across two points in said first named circuit element.

5. An attenuator comprising two pairs of resisters, means for applying a signal voltage across two points between the ends of one pair, means conductively connecting the ends of one pair, and two adjustable contacts, one being arranged to slide along each pair of said resistors.

6. The device of the preceding claim in combination with a uni-control means for simultaneously operating said adjustable contacts.

7. In combination in a device of the class described, a phonograph signal source, a radio signal source, and a source of speech frequency, an attenuator having three sections one connected to each of said signal sources, a common output circuit connected to said attenuator sections, means comprising two slidable contacts adjustable along any one of said attenuator sectionswhereby currents from either of said named signal sources and of any desired amplitude may be secured in said output circuit and a single control shaft arranged to operate said slidable contacts.

8. In combination in a device of the class described, a phonograph signal source, a radio signal source, and a source of speech frequency, a mixer connected to each of said sources andhaving an output circuit, adjustable means included in said mixer whereby the voltage applied to said output circuit by said phonograph source may be adjustably controlled and additional means comprised in said mixer whereby substantially the full voltage developed by said speech frequency source is applied to said output circuit as said means is adjusted.

9. In combination, a phonograph signal source, a radio signal source, asource of speech frequency, an attenuator connected to each of said sources and having an output circuit, said attenuator comprising adjustable means for attenuating the currents from either said phonograph or said radio sources and means for simultaneously maintaining at substantially constant volume level in said output circuit the currents from said speech frequency source.

10. In combination in an attenuator, two resistors spaced apart and in parallel relation, a conductive contact resting against said resistors, two conductive strips one connected to each of said resistors, a conductive slider in contact with said strips and uni-control means for actuating said slider and contact.

11. In an attenuator device, the combination of a casing, two concentrically arranged resistor elements mounted in said casing, two conductor elements mounted within said casing, connections between said conductor elements and said resistors, a contact member adjustable along said resistor elements, a separate contact member adjustable along said conductor elements and means connected to operate said contact members simultaneously.

12. The combination defined in the preceding claim in which said last named means comprises a shaft extending through said casing and a control handle secured to said shaft.

13. In a device of the class described, the combination of a phonograph signal source, a radio signal source, and a source of speech frequency, an attenuator connected to each of said sources and having an output circuit, adjustable means included in said attenuator whereby the voltage applied to said output circuit by said radio signal source may be adjustably controlled and additional means comprised in said attenuator whereby substantially the full voltage developed by said speech frequency source is applied to said output circuit as said means is adjusted.

14. In an attenuator device, the combination of three concentrically arranged insulating strips, resistor elements mounted on two of said strips, 2. pair of conductors of low resistance mounted on the third of said strips, conductive connections between said resistor elements and said pair of conductors, a shaft, an arm secured to said shaft, a pair of contact members secured to said arm, one of said members being in engagement with said resistor elements and the other contact member being arranged to engage said pair of conductors and a shielding casing arranged to enclose the aforesaid attenuator device.

15. In an attenuator device, the combination of a casing, two substantially parallelly arranged resistors mounted in said casing, two conductors mounted in said casing substantially parallel to said resistors, leads connecting said resistors to said respective conductors, a contact member adjustable along said resistors, a second contact member adjustable along said conductors and a single operating means projecting through said casing and mechanically connected within said casing to both of said contact members.

ALVA R. HOPKINS. 

